Github user sethah commented on the issue:

    https://github.com/apache/spark/pull/13621
  
    @avulanov 
    
    I used this implementation to run a simple single layer autoencoder on the 
MNIST dataset. I also used keras/theano to implement the same autoencoder and 
run on the MNIST data. With Spark, I got very poor results. First, here are the 
results of encode/decode using Keras with a cross entropy loss function on the 
output, and sigmoid activations. 
    
    
![image](https://cloud.githubusercontent.com/assets/7275795/17375073/59b14faa-5964-11e6-943f-d2e1db06089d.png)
    
    The implementation in this patch yielded very similar results.
    
    
![image](https://cloud.githubusercontent.com/assets/7275795/17374543/fb923c42-5961-11e6-8c97-dfa7626c4cc3.png)
    
    Finally, here is the Keras implementation using RELU activations.
    
    
![image](https://cloud.githubusercontent.com/assets/7275795/17375464/ebe1b8d2-5965-11e6-964f-fa8cc1c2a4f5.png)
    
    It appears the sigmoid activations are saturating during training and 
preventing the algorithm from learning. If you have any thoughts/suggestions to 
improve these results I'd really appreciate it.
    
    Does it make sense to add another algorithm based on MLP/NN when the 
current functionality is so limited? If the autoencoder library is not useful 
without more than sigmoid activations, I'd vote for focusing on adding new 
activations before another algorithm. I'm not an expert here, so I would really 
appreciate your thoughts. Thanks!


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